EP0799439B1 - Positioning device with a force actuator system for compensating centre-of-gravity displacements - Google Patents

Description

• The invention relates to a positioning device with an object table and adrive unit by which the object table is displaceable parallel to at least an X-direction over aguide which is fastened to a frame of the positioning device.
• The invention also relates to a lithographic device with a machine framewhich, seen parallel to a vertical Z-direction, supports in that order a radiation source, amask holder, a focusing system with a main axis directed parallel to the Z-direction, and asubstrate holder which is displaceable perpendicularly to the Z-direction by means of apositioning device.
• The invention further relates to a lithographic device with a machineframe which, seen parallel to a vertical Z-direction, supports in that order a radiation source,a mask holder which is displaceable perpendicularly to the Z-direction by means of apositioning device, a focusing system with a main axis directed parallel to the Z-direction,and a substrate holder which is displaceable perpendicularly to the Z-direction by means of afurther positioning device.
• A positioning device of the kind mentioned in the opening paragraph isknown from US Patent 5,260,580. The known positioning device comprises an object tablewhich is supported by and guided over a stationary base which in its turn is supported by afirst frame. The known positioning device comprises a drive unit for displacing the objecttable over the stationary base. The drive unit has a first linear motor of which a stationarypart is supported by the stationary base and a second linear motor of which a stationary partis supported by a second frame. The second frame is dynamically isolated from the firstframe, so that mechanical forces and vibrations present in the second frame cannot betransmitted to the first frame. The object table of the known positioning device isdisplaceable during operation by means of the second linear motor into a position which liesclose to a desired end position, whereupon it can be moved into the desired end position bythe first linear motor. The displacement of the object table by the second linear motor isusually a comparatively great, speed-controlled displacement during which the second linear motor exerts a comparatively great driving force on the object table. The subsequentdisplacement of the object table by the first linear motor is a comparatively small, position-controlleddisplacement during which the first linear motor exerts a comparatively smalldriving force on the object table. Since the stationary part of the second linear motor issupported by the second frame which is dynamically isolated from the first frame, it isprevented that a comparatively great reaction force exerted by the object table on the secondlinear motor and arising from the driving force exerted by the second linear motor on theobject table, as well as mechanical vibrations caused by the reaction force in the secondframe are transmitted into the first frame, the stationary base, and the object table.Furthermore, the first frame of the known positioning device can be placed on a floor surfaceby means of a number of dampers which have a comparatively low mechanical stiffness.Owing to the low mechanical stiffness of the dampers, mechanical vibrations present in thefloor cannot be transmitted into the first frame. The fact that the stationary base and theobject table of the known positioning device thus remain free from said vibrations present inthe floor and from the comparatively strong mechanical vibrations caused by the secondlinear motor means that the object table is displaceable into the desired end position in aquick and accurate manner by means of the first linear motor.
• A disadvantage of the known positioning device is that the first framewill be brought into vibration or will start shaking on said dampers when the object table isdisplaced over comparatively great distances relative to the stationary base. The object tablerests on the stationary base with a support force which is determined by a force of gravityacting on the object table. When the object table is displaced relative to the stationary base, apoint of application of said support force on the stationary base is also displaced relative tothe stationary base. Since displacements of the object table over comparatively greatdistances usually take place with comparatively low frequencies and the stationary base islow-frequency spring-supported relative to the floor by means of said dampers, thedisplacements of the point of application of the support force arising from said comparativelygreat displacements of the object table will lead not only to mechanical vibrations in thestationary base and the first frame, but also to a low-frequency shaking movement of the firstframe on the dampers. Such mechanical vibrations and shaking movements deteriorate thepositioning accuracy and the positioning time of the positioning device, i.e. the accuracy withwhich and the time span within which a desired end position is reached.
• It is an object of the invention to provide a positioning device of the kind mentioned in the opening paragraph with which the above disadvantage is prevented as muchas possible.
• The invention is for this purpose characterized in that the positioningdevice is provided with a force actuator system controlled by an electric controller andexerting a compensation force on the frame during operation, which compensation force hasa mechanical moment about a reference point of the frame having a value equal to a value ofa mechanical moment of a force of gravity acting on the object table about said referencepoint, and a direction which is opposed to a direction of the mechanical moment of said forceof gravity. The controller controls the compensation force of the force actuator system as afunction of a position of the object table relative to the stationary base. The controller isprovided with, for example, a feedforward control loop in which the controller receivesinformation on the position of the object table from an electric control unit of the positioningdevice, or with a feedback control loop in which the controller receives information on theposition of the object table from a position sensor. The use of said force actuator systemrenders a sum of the moment of said force of gravity and the moment of the compensationforce about the reference point of the frame constant as much as possible. As a result, thedisplaceable object table has a so-called virtual centre of gravity which has a substantiallyconstant position relative to the frame, so that the frame in effect does not sense thedisplacements of the point of application of the support force of the object table. Mechanicalvibrations and low-frequency shaking movements of the frame owing to displacements of theactual centre of gravity of the object table are thus prevented, whereby an improvement inthe positioning accuracy and positioning time of the positioning device is achieved.
• A further embodiment of a positioning device according to the inventionis characterized in that the object table is displaceable parallel to a horizontal direction, whilethe force actuator system exerts the compensation force on the frame parallel to a verticaldirection. Since the force actuator system exerts the compensation force on the frame parallelto the vertical direction, the force actuator system does not exert forces on the frame in adrive direction of the object table, so that the force actuator system causes no mechanicalvibrations in the frame directed parallel to the drive direction, and no measures need betaken to prevent such vibrations. Vertical vibrations of the frame are prevented in that avalue of the compensation force of the force actuator system is kept constant and in thatexclusively a point of application of the compensation force on the frame is displaced as afunction of the position of the object table. The displacement of the point of application ofthe compensation force of the force actuator system is achieved, for example, through the use of a force actuator system with at least two separate force actuators wherein thecompensation forces of the force actuators are individually controlled as a function of theposition of the object table, a sum of the compensation forces of the separate force actuatorsbeing kept constant.
• A still further embodiment of a positioning device according to theinvention is characterized in that the object table is displaceable parallel to a horizontal X-directionand parallel to a horizontal Y-direction which is perpendicular to the X-direction,while the force actuator system comprises three force actuators mutually arranged in atriangle and each exerting a compensation force on the frame parallel to the verticaldirection. The use of the force actuator system with the three force actuators mutuallyarranged in a triangle not only prevents mechanical vibrations of the frame arising from adisplacement of the object table parallel to the X-direction, but also prevents mechanicalvibrations of the frame arising from a displacement of the object table parallel to the Y-direction.The sum of the compensation forces of the individual force actuators is keptconstant continually during operation, so that the force actuator system causes no verticalvibrations in the frame. The triangular arrangement of the force actuators in additionprovides a particularly stable operation of the force actuator system.
• A special embodiment of a positioning device according to the inventionis characterized in that the force actuator system is integrated with a system of dynamicisolators by means of which the frame is coupled to a base of the positioning device. Thedynamic isolators are, for example, dampers with a comparatively low mechanical stiffnessby means of which the frame is dynamically isolated from said base. Owing to thecomparatively low mechanical stiffness of the dampers, mechanical vibrations present in thebase such as, for example, floor vibrations are not transmitted into the frame. The integrationof the force actuator system with the system of dynamic isolators provides a particularlycompact and simple construction of the positioning device.
• A further embodiment of a positioning device according to the inventionis characterized in that the compensation force comprises exclusively a Lorentz force of amagnet system and an electric coil system of the force actuator system. The force actuatorsystem comprises a part which is fastened to the frame and a part which is fastened to a baseof the positioning device. Since the compensation force of the force actuator systemcomprises exclusively a Lorentz force, said parts of the force actuator system are physicallydecoupled, i.e. there is no physical contact or physical coupling between said parts. It isprevented thereby that mechanical vibrations present in the base of the positioning device such as, for example, floor vibrations are transmitted into the frame and the object table viathe force actuator system.
• A lithographic device with a displaceable substrate holder of the kindmentioned in the opening paragraphs is known from EP-A-0 498 496. The knownlithographic device is used in the manufacture of integrated semiconductor circuits by meansof an optical lithographic process. The radiation source of the known lithographic device is alight source, while the focusing system is an optical lens system by means of which a partialpattern of an integrated semiconductor circuit, which pattern is present on a mask which canbe placed on the mask holder of the lithographic device, is imaged on a reduced scale on asemiconductor substrate which can be placed on the substrate holder of the lithographicdevice. Such a semiconductor substrate comprises a large number of fields on which identicalsemiconductor circuits are provided. The individual fields of the semiconductor substrate areconsecutively exposed for this purpose, the semiconductor substrate being in a constantposition relative to the mask and the focusing system during the exposure of an individualfield, while between two consecutive exposure steps a next field of the semiconductorsubstrate is brought into position relative to the focusing system by means of the positioningdevice of the substrate holder. This process is repeated a number of times, each time with adifferent mask with a different partial pattern, so that integrated semiconductor circuits ofcomparatively complicated structure can be manufactured. The structures of such integratedsemiconductor circuits have detail dimensions which lie in the sub-micron range. The partialpatterns present on the consecutive masks should accordingly be imaged on said fields of thesemiconductor substrate with an accuracy relative to one another which lies in the sub-micronrange. The semiconductor substrate should accordingly be positioned relative to the mask andthe focusing system by means of the positioning device of the substrate holder with anaccuracy also in the sub-micron range. To reduce the time required for the manufacture ofthe semiconductor circuits, moreover, the semiconductor substrate should be displaced with acomparatively high speed between two consecutive exposure steps and should be positionedrelative to the mask and the focusing system with the desired accuracy.
• According to the invention, the lithographic device with the displaceablesubstrate holder is characterized in that the positioning device of the substrate holder is apositioning device according to the invention wherein the frame of the positioning device ofthe substrate holder belongs to the machine frame of the lithographic device, while the forceactuator system of the positioning device of the substrate holder exerts the compensationforce on the machine frame. The use of the positioning device according to the invention with said force actuator system prevents shaking or vibrating of the machine frame of thelithographic device when the substrate holder with the semiconductor substrate is moved at acomparatively high speed to a next field by the positioning device between two consecutiveexposure steps, during which the centre of gravity of the substrate holder is displaced relativeto the machine frame of the lithographic device. The controlier of the force actuator systemcontrols the compensation force as a function of a position of the substrate holder relative tothe machine frame. Owing to the use of the force actuator system, a sum of a moment of aforce of gravity acting on the substrate holder and a moment of the compensation force aboutthe reference point of the machine frame remains constant as much as possible, so that themachine frame senses the displacements of the centre of gravity of the substrate holder aslittle as possible. Mechanical vibrations of the machine frame caused by displacements of thecentre of gravity of the substrate holder are prevented thereby, so that the accuracy withwhich the substrate holder can be positioned relative to the machine frame and the timerequired for the positioning process are not adversely affected by such displacements of thecentre of gravity.
• A lithographic device with a displaceable substrate holder and adisplaceable mask holder of the kind mentioned in the opening paragraphs is known from USPatent 5,194,893. In this known lithographic device, the semiconductor substrate undermanufacture is not in a constant position relative to the mask and the focusing system duringthe exposure of a single field of the semiconductor substrate, but instead the semiconductorsubstrate and the mask are synchronously displaced relative to the focusing system parallel toan X-direction which is perpendicular to the Z-direction by means of the positioning deviceof the substrate holder and the positioning device of the mask holder, respectively, duringexposure. In this manner the pattern present on the mask is scanned parallel to the X-directionand synchronously imaged on the semiconductor substrate. It is achieved therebythat a maximum surface area of the mask which can be imaged on the semiconductorsubstrate by means of the focusing system is limited to a lesser degree by a size of anaperture of the focusing system. Since the detail dimensions of the integrated semiconductorcircuits to be manufactured lie in the sub-micron range, the semiconductor substrate and themask should be displaced with an accuracy also in the sub-micron range relative to thefocusing system during the exposure. To reduce the time required for the manufacture of thesemiconductor circuits, the semiconductor substrate and the mask should in addition bedisplaced and positioned relative to one another with a comparatively high speed duringexposure. Since the pattern present on the mask is imaged on a reduced scale on the semiconductor substrate, the speed with which and the distance over which the mask isdisplaced are greater than the speed with which and the distance over which thesemiconductor substrate is displaced, the ratio between said speeds and the ratio between saiddistances both being equal to a reduction factor of the focusing system.
• According to the invention, the lithographic device with the displaceablesubstrate holder and displaceable mask holder is characterized in that the positioning deviceof the mask holder is a positioning device according to the invention wherein the frame ofthe positioning device of the mask holder belongs to the machine frame of the lithographicdevice, while the force actuator system of the positioning device of the mask holder exertsthe compensation force on the machine frame.
• A special embodiment of a lithographic device with a displaceablesubstrate holder according to the invention is characterized in that the mask holder isdisplaceable perpendicularly to the Z-direction by means of a positioning device according tothe invention wherein the frame of the positioning device of the mask holder belongs to themachine frame of the lithographic device, while the force actuator system of the positioningdevice of the mask holder exerts the compensation force on the machine frame.
• It is prevented thereby that the machine frame of the lithographic devicewill vibrate or shake when the mask holder with the mask is moved over comparatively greatdistances by the positioning device during the exposure of the semiconductor substrate,during which the centre of gravity of the mask holder is displaced over comparatively greatdistances relative to the machine frame of the lithographic device. Mechanical vibrations ofthe machine frame arising from the comparatively great displacements of the centre ofgravity of the mask holder are thus prevented during the exposure of the semiconductorsubstrate, so that the accuracy with which the substrate holder and the mask holder can bepositioned relative to the machine frame during the exposure of the semiconductor substrateand the time required for positioning are not adversely affected by such comparatively greatdisplacements of the centre of gravity of the mask holder.
• A further embodiment of a lithographic device according to the inventionis characterized in that the positioning devices of the substrate holder and the mask holderhave a joint force actuator system such that the value of the mechanical moment of thecompensation force of the joint force actuator system about the reference point is equal to avalue of a sum of a mechanical moment of a force of gravity acting on the substrate holderabout said reference point and a mechanical moment of a force of gravity acting on the maskholder about said reference point, while the direction of the mechanical moment of the compensation force is opposed to a direction of said sum of mechanical moments. Thecontroller of the force actuator system here controls the compensation force as a function ofthe position of the mask holder and the position of the substrate holder relative to themachine frame, so that the joint force actuator system compensates both displacements of thecentre of gravity of the mask holder and displacements of the centre of gravity of thesubstrate holder. The construction of the lithographic device is simplified by the use of thejoint force actuator system.
• A yet further embodiment of a lithographic device according to theinvention is characterized in that the machine frame is placed on a base of the lithographicdevice by means of three dynamic isolators mutually arranged in a triangle, while t1.e forceactuator system comprises three separate force actuators which are each integrated with acorresponding one of the dynamic isolators. The dynamic isolators are, for example, damperswith a comparatively low mechanical stiffness by means of which the machine frame isdynamically isolated from said base. Owing to the comparatively low mechanical stiffness ofthe dampers, mechanical vibrations present in the base such as, for example, floor vibrationsare not transmitted to the machine frame. The integration of the force actuator system withthe system of dynamic isolators provides a particularly compact and simple construction ofthe lithographic device. The triangular arrangement of the isolators in addition provides aparticularly stable support for the machine frame.
• The invention will be explained in more detail below with reference tothe drawing, in which
• Fig. 1 shows a lithographic device according to the invention,
• Fig. 2 is a diagram of the lithographic device of Fig. 1,
• Fig. 3 shows a base and a substrate holder of the lithographic device ofFig. 1,
• Fig. 4 is a plan view of the base and the substrate holder of thelithographic device of Fig. 3,
• Fig. 5 is a plan view of a mask holder of the lithographic device of Fig.1,
• Fig. 6 is a cross-section taken on the line VI-VI in Fig. 5,
• Fig. 7 is a cross-section of a dynamic isolator of the lithographic deviceof Fig. 1,
• Fig. 8 is a cross-section taken on the line VIII-VIII in Fig. 7, and
• Fig. 9 diagrammatically shows a force actuator system of the lithographicdevice of Fig. 1.
• The lithographic device according to the invention shown in Figs. 1 and2 is used for the manufacture of integrated semiconductor circuits by an optical lithographicprocess. As Fig. 2 shows diagrammatically, the lithographic device is consecutivelyprovided, seen parallel to a vertical Z-direction, with asubstrate holder 1, a focusing system3, amask holder 5, and a radiation source 7. The lithographic device shown in Figs. 1 and 2is an optical lithographic device in which the radiation source 7 comprises a light source 9, adiaphragm 11, and mirrors 13 and 15. Thesubstrate holder 1 comprises asupport surface 17which extends perpendicularly to the Z-direction and on which asemiconductor substrate 19can be placed, while it is displaceable relative to the focusing system 3 parallel to an X-directionperpendicular to the Z-direction and parallel to a Y-direction which is perpendicularto the X-direction and the Z-direction by means of afirst positioning device 21 of thelithographic device. The focusing system 3 is an imaging or projection system and comprisesa system of optical lenses 23 with an opticalmain axis 25 which is parallel to the Z-directionand an optical reduction factor which is, for example, 4 or 5. Themask holder 5 comprises asupport surface 27 which is perpendicular to the Z-direction and on which amask 29 can beplaced, while it is displaceable parallel to the X-direction relative to the focusing system 3 bymeans of asecond positioning device 31 of the lithographic device. Themask 29 comprises apattern or partial pattern of an integrated semiconductor circuit. During operation, alightbeam 33 originating from the light source 9 is passed through themask 29 via the diaphragm11 and themirrors 13, 15 and is focused on thesemiconductor substrate 19 by means of thelens system 23, so that the pattern present on themask 29 is imaged on a reduced scale onthesemiconductor substrate 19. Thesemiconductor substrate 19 comprises a large number ofindividual fields 35 on which identical semiconductor circuits are provided. For this purpose,thefields 35 of thesemiconductor substrate 19 are consecutively exposed through themask29, anext field 35 being positioned relative to the focusing system 3 each time after theexposure of anindividual field 35 in that thesubstrate holder 1 is moved parallel to the X-directionor the Y-direction by means of thefirst positioning device 21. This process isrepeated a number of times, each time with a different mask, so that comparativelycomplicated integrated semiconductor circuits with a layered structure are manufactured.
• As Fig. 2 shows, thesemiconductor substrate 19 and themask 29 aresynchronously displaced relative to the focusing system 3 parallel to the X-direction by the first and thesecond positioning device 21, 31 during the exposure of anindividual field 35.The pattern present on themask 29 is thus scanned parallel to the X-direction andsynchronously imaged on thesemiconductor substrate 19. In this way, as is clarified in Fig.2, exclusively a maximum width B of themask 29 directed parallel to the Y-direction whichcan be imaged on thesemiconductor substrate 19 by the focusing system 3 is limited by adiameter D of anaperture 37 of the focusing system 3 diagrammatically depicted in Fig. 2.An admissible length L of themask 29 which can be imaged on thesemiconductor substrate19 by the focusing system 3 is greater than said diameter D. In this imaging method, whichfollows the so-called "step and scan" principle, a maximum surface area of themask 29which can be imaged on thesemiconductor substrate 19 by the focusing system 3 is limitedby the diameter D of theaperture 37 of the focusing system 3 to a lesser degree than in aconventional imaging method which follows the so-called "step and repeat" principle, whichis used, for example, in a lithographic device known from EP-A-0 498 496, where the maskand the semiconductor substrate are in fixed positions relative to the focusing system duringexposure of the semiconductor substrate. Since the pattern present on themask 29 is imagedon a reduced scale on thesemiconductor substrate 19, said length L and width B of themask29 are greater than a corresponding length L' and width B' of thefields 35 on thesemiconductor substrate 19, a ratio between the lengths L and L' and between the widths Band B' being equal to the optical reduction factor of the focusing system 3. As a result also,a ratio between a distance over which themask 29 is displaced during exposure and adistance over which thesemiconductor substrate 19 is displaced during exposure, and a ratiobetween a speed with which themask 29 is displaced during exposure and a speed withwhich thesemiconductor substrate 19 is displaced during exposure are both equal to theoptical reduction factor of the focusing system 3. In the lithographic device shown in Fig. 2,the directions in which thesemiconductor substrate 19 and themask 29 are displaced duringexposure are mutually opposed. It is noted that said directions may also be the same if thelithographic device comprises a different focusing system by which the mask pattern is notimaged in reverse.
• The integrated semiconductor circuits to be manufactured with thelithographic device have a structure with detail dimensions in the sub-micron range. Since thesemiconductor substrate 19 is exposed consecutively through a number of different masks,the patterns present on the masks must be imaged on thesemiconductor substrate 19 relativeto one another with an accuracy which is also in the sub-micron range, or even in thenanometer range. During exposure of thesemiconductor substrate 19, thesemiconductor substrate 19 and themask 29 should accordingly be displaced relative to the focusing system3 with such an accuracy, so that comparatively high requirements are imposed on thepositioning accuracy of the first and thesecond positioning device 21, 31.
• As Fig. 1 shows, the lithographic device has a base 39 which can beplaced on a horizontal floor surface. The base 39 forms part of aforce frame 41 to whichfurther a vertical, comparativelystiff metal column 43 belongs which is fastened to thebase39. The lithographic device further comprises amachine frame 45 with a triangular,comparatively stiff metalmain plate 47 which extends transversely to the opticalmain axis25 of the focusing system 3 and is provided with a central light passage opening not visiblein Fig. 1. Themain plate 47 has threecorner portions 49 with which it rests on threedynamic isolators 51 which are fastened on thebase 49 and which will be described furtherbelow. Only twocorner portions 49 of themain plate 47 and twodynamic isolators 51 arevisible in Fig. 1, while all threedynamic isolators 51 are visible in Figs. 3 and 4. Thefocusing system 3 is provided near a lower side with a mountingring 53 by means of whichthe focusing system 3 is fastened to themain plate 47. Themachine frame 45 also comprisesa vertical, comparativelystiff metal column 55 fastened on themain plate 47. Near an upperside of the focusing system 3 there is furthermore asupport member 57 for themask holder5, which member also belongs to themachine frame 45, is fastened to thecolumn 55 of themachine frame 45, and will be explained further below. Also belonging to themachine frame45 are threevertical suspension plates 59 fastened to a lower side of themain plate 47adjacent the threerespective corner portions 49. Only twosuspension plates 59 are partlyvisible in Fig. 1, while all threesuspension plates 59 are visible in Figs. 3 and 4. As Fig. 4shows, ahorizontal support plate 61 for thesubstrate holder 1 also belonging to themachineframe 45 is fastened to the threesuspension plates 59. Thesupport plate 61 is not visible inFig. 1 and only partly visible in Fig. 3.
• It is apparent from the above that themachine frame 45 supports themain components of the lithographic device, i.e. thesubstrate holder 1, the focusing system3, and themask holder 5 parallel to the vertical Z-direction. As will be further explainedbelow, thedynamic isolators 51 have a comparatively low mechanical stiffness. It is achievedthereby that mechanical vibrations present in the base 39 such as, for example, floorvibrations are not transmitted into themachine frame 45 via thedynamic isolators 51. Thepositioning devices 21, 31 as a result have a positioning accuracy which is not adverselyaffected by the mechanical vibrations present in thebase 39. The function of theforce frame41 will be explained in more detail further below.
• As Figs. 1 and 5 show, themask holder 5 comprises ablock 63 onwhich saidsupport surface 27 is present. Thesupport member 57 for themask holder 5belonging to themachine frame 45 comprises a central light passage opening 64 visible inFig. 5 and two plane guides 65 which extend parallel to the X-direction and which lie in acommon plane which is perpendicular to the Z-direction. Theblock 63 of themask holder 5is guided over the plane guides 65 of thesupport member 57 by means of an aerostaticbearing (not visible in the Figures) with freedoms of movement parallel to the X-directionand parallel to the Y-direction, and a freedom of rotation about an axis ofrotation 67 of themask holder 5 which is directed parallel to the Z-direction.
• As Figs. 1 and 5 further show, thesecond positioning device 31 bywhich themask holder 5 is displaceable comprises a firstlinear motor 69 and a secondlinearmotor 71. The secondlinear motor 71, which is of a kind usual and known per se, comprisesastationary part 73 which is fastened to thecolumn 43 of theforce frame 41. Thestationarypart 73 comprises aguide 75 which extends parallel to the X-direction and along which amovable part 77 of the secondlinear motor 71 is displaceable. Themovable part 77comprises aconnection arm 79 which extends parallel to the Y-direction and to which anelectric coil holder 81 of the firstlinear motor 69 is fastened. A permanent-magnet holder 83of the firstlinear motor 69 is fastened to theblock 63 of themask holder 5. The firstlinearmotor 69 is of a kind known from EP-B-0 421 527. As Fig. 5 shows, thecoil holder 81 ofthe firstlinear motor 69 comprises fourelectric coils 85, 87, 89, 91 which extend parallel tothe Y-direction, and anelectric coil 93 which extends parallel to the X-direction. Thecoils85, 87, 89, 91, 93 are diagrammatically indicated with broken lines in Fig. 5. Themagnetholder 83 comprises ten pairs of permanent magnets (95a, 95b), (97a, 97b), (99a, 99b),(101a, 101b), (103a, 103b), (105a, 105b), (107a, 107b), (109a, 109b), (111a, 111b), (113a,113b), indicated with dash-dot lines in Fig. 5. Theelectric coil 85 and thepermanentmagnets 95a, 95b, 97a and 97b belong to afirst X-motor 115 of the firstlinear motor 69,while thecoil 87 and themagnets 99a, 99b, 101a and 101b belong to asecond X-motor 117of the firstlinear motor 69, thecoil 89 and themagnets 103a, 103b, 105a and 105b belongto a third X-motor 119 of the firstlinear motor 69, thecoil 91 and themagnets 107a, 107b,109a and 109b belong to afourth X-motor 121 of the firstlinear motor 69, and thecoil 93and themagnets 111a, 111b, 113a and 113b belong to a Y-motor 123 of the firstlinearmotor 69. Fig. 6 is a cross-sectional view of the first X-motor 115 and thesecond X-motor117. As Fig. 6 shows, thecoil holder 81 is arranged between afirst part 125 of themagnetholder 83 which comprises themagnets 95a, 97a, 99a, 101a, 103a, 105a, 107a, 109a, 111a and 113a, and asecond part 127 of the magnet holder which comprises themagnets 95b,97b, 99b, 101b, 103b, 105b, 107b, 109b, 111b and 113b. As Fig. 6 further shows, themagnet pair 95a, 95b of the first X-motor 115 and themagnet pair 99a, 99b of the second X-motor117 are magnetized parallel to a positive Z-direction, while themagnet pair 97a, 97bof the first X-motor 115 and themagnet pair 101a, 101b of the second X-motor 117 aremagnetized parallel to an opposed, negative Z-direction. Thus also themagnet pair 103a,103b of the third X-motor 119, themagnet pair 107a, 107b of the fourth X-motor 121, andthemagnet pair 111a, 111b of the Y-motor 123 are magnetized parallel to the positive Z-direction,whereas themagnet pair 105a, 105b of the third X-motor 119, themagnet pair109a, 109b of the fourth X-motor 121, and themagnet pair 113a, 113b of the Y-motor 123are magnetized parallel to the negative Z-direction. As Fig. 6 further shows, themagnets 95aand 97a of the first X-motor 115 are interconnected by amagnetic closing yoke 129, whilethemagnets 95b and 97b, themagnets 99a and 101a, and themagnets 99b and 101b areinterconnected by means of amagnetic closing yoke 131, amagnetic closing yoke 133, and amagnetic closing yoke 135, respectively. The third X-motor 119, the fourth X-motor 121,and the Y-motor 123 are provided with similar magnetic closing yokes. When duringoperation an electric current flows through thecoils 85, 87, 89, 91 of theX-motors 115,117, 119, 121, the magnets and coils of theX-motors 115, 117, 119, 121 mutually exert aLorentz force directed parallel to the X-direction. If the electric currents through thecoils85, 87, 89, 91 are of equal value and direction, themask holder 5 is displaced parallel to theX-direction by said Lorentz force, whereas themask holder 5 is rotated about the axis ofrotation 67 if the electric currents through thecoils 85, 87 are of equal value as, but have adirection opposed to the electric currents through thecoils 89, 91. The magnets and the coilof the Y-motor 123 mutually exert a Lorentz force directed parallel to the Y-direction as aresult of an electric current through thecoil 93 of the Y-motor 123, whereby themask holder5 is displaced parallel to the Y-direction.
• During exposure of thesemiconductor substrate 19, themask holder 5should be displaced relative to the focusing system 3 parallel to the X-direction over acomparatively great distance and with a high positioning accuracy. To achieve this, thecoilholder 81 of the firstlinear motor 69 is displaced parallel to the X-direction by means of thesecondlinear motor 71, a desired displacement of themask holder 5 being approximatelyachieved by the secondlinear motor 71, and themask holder 5 being carried along relativeto themovable part 77 of the secondlinear motor 71 by a suitable Lorentz force of theX-motors115, 117, 119, 121 of the firstlinear motor 69. Said desired displacement of themask holder 5 relative to the focusing system 3 is achieved in that the Lorentz force of theX-motors 115, 117, 119, 121 is controlled by means of a suitable position control systemduring the displacement of themask holder 5. The position control system, which is notshown in any detail in the Figures, comprises, for example, a laser interferometer which isusual and known per se for measuring the position of themask holder 5 relative to thefocusing system 3, whereby the desired positioning accuracy in the sub-micron or nanometerrange is achieved. During the exposure of thesemiconductor substrate 19, the firstlinearmotor 69 not only controls the displacement of themask holder 5 parallel to the X-direction,but it also controls a position of themask holder 5 parallel to the Y-direction and an angle ofrotation of themask holder 5 about the axis ofrotation 67. Since themask holder 5 can alsobe positioned parallel to the Y-direction and rotated about the axis ofrotation 67 by the firstlinear motor 69, the displacement of themask holder 5 has a parallelism relative to the X-directionwhich is determined by the positioning accuracy of the firstlinear motor 69.Deviations from parallelism of theguide 75 of the secondlinear motor 71 relative to the X-directioncan thus be compensated through displacements of themask holder 5 parallel to theY-direction. Since the desired displacement of themask holder 5 need be achievedapproximately only by the secondlinear motor 71, and no particularly high requirements areimposed on the parallelism of theguide 75 relative to the X-direction, a comparativelysimple, conventional, one-dimensional linear motor can be used as the secondlinear motor71, by means of which themask holder 5 is displaceable over comparatively large distanceswith a comparatively low accuracy. The desired accuracy of the displacement of themaskholder 5 is achieved in that themask holder 5 is displaced over comparatively small distancesrelative to themovable part 77 of the secondlinear motor 71 by means of the firstlinearmotor 69. The firstlinear motor 69 is of comparatively small dimensions because thedistances over which themask holder 5 is displaced relative to themovable part 77 of thesecondlinear motor 71 are only small. Electrical resistance losses in the electric coils of thefirstlinear motor 69 are minimized thereby.
• As was noted above, thestationary part 73 of the secondlinear motor 71is fastened to theforce frame 41 of the lithographic device. It is achieved thereby that areaction force exerted by themovable part 77 of the secondlinear motor 71 on thestationarypart 73 and arising from a driving force of the secondlinear motor 71 exerted on themovable part 77 is transmitted into theforce frame 41. Since furthermore thecoil holder 81of the firstlinear motor 69 is fastened to themovable part 77 of the secondlinear motor 71,a reaction force exerted by themask holder 5 on themovable part 77 and arising from a Lorentz force of the firstlinear motor 69 exerted on themask holder 5 is also transmittedinto theforce frame 41 via themovable part 77 and thestationary part 73 of the secondlinear motor 71. A reaction force exerted during operation by themask holder 5 on thesecond positioning device 31 and arising from a driving force exerted on themask holder 5by thesecond positioning device 31 is thus introduced exclusively into theforce frame 41.Said reaction force has a low-frequency component resulting from the comparatively greatdisplacements of the secondlinear motor 71 as well as a high-frequency component resultingfrom the comparatively small displacements carried out by the firstlinear motor 69 in orderto achieve the desired positioning accuracy. Since theforce frame 41 is comparatively stiffand is placed on a solid base, the mechanical vibrations caused by the low-frequencycomponent of the reaction force in theforce frame 41 are negligibly small. The high-frequencycomponent of the reaction force does have a small value, but it usually has afrequency which is comparable to a resonance frequency characteristic of a type of framesuch as theforce frame 41 used. As a result, the high-frequency component of the reactionforce causes a non-negligible high-frequency mechanical vibration in theforce frame 41. Theforce frame 41 is dynamically isolated from themachine frame 45, i.e. mechanical vibrationshaving a frequency above a certain threshold value, for example 10 Hz, present in theforceframe 41 are not transmitted into themachine frame 45, because the latter is coupled to theforce frame 41 exclusively via the low-frequencydynamic isolators 51. It is achieved therebythat the high-frequency mechanical vibrations caused in theforce frame 41 by the reactionforces of thesecond positioning device 31 are not transmitted into themachine frame 45,similar to the floor vibrations mentioned above. Since the plane guides 65 of thesupportmember 57 extend perpendicularly to the Z-direction, and the driving forces exerted by thesecond positioning device 31 on themask holder 5 are also directed perpendicularly to the Z-direction,said driving forces themselves do not cause any mechanical vibrations in themachine frame 45 either. Furthermore, the mechanical vibrations present in theforce frame41 cannot be transmitted into themachine frame 45 through thestationary part 73 and themovable part 77 of the secondlinear motor 71 either because, as is apparent from the above,themask holder 5 is coupled to themovable part 77 of the secondlinear motor 71substantially exclusively by Lorentz forces of the magnet system and the electric coil systemof the firstlinear motor 69, and themask holder 5 is physically decoupled from themovablepart 77 of the secondlinear motor 71, apart from said Lorentz forces. So the abovediscussion shows that themachine frame 45 remains substantially free from mechanicalvibrations and deformations caused by the driving forces and reaction forces of thesecond positioning device 31. The advantages thereof will be further discussed below.
• As Figs. 3 and 4 show, thesubstrate holder 1 comprises ablock 137 onwhich saidsupport surface 17 is present, and an aerostatically supportedfoot 139 which isprovided with an aerostatic bearing. Thesubstrate holder 1 is guided over anupper surface141, which extends perpendicularly to the Z-direction, of agranite support 143 provided onthesupport plate 61 of themachine frame 45 by means of the aerostatically supportedfoot139, and has freedoms of displacement parallel to the X-direction and parallel to the Y-direction,and a freedom of rotation about an axis ofrotation 145 of thesubstrate holder 1which is directed parallel to the Z-direction.
• As Figs. 1, 3 and 4 further show, thepositioning device 21 of thesubstrate holder 1 comprises a firstlinear motor 147, a secondlinear motor 149, and a thirdlinear motor 151. The secondlinear motor 149 and the thirdlinear motor 151 of thepositioning device 21 are of a kind identical to the secondlinear motor 71 of thepositioningdevice 31. The secondlinear motor 149 comprises astationary part 153 fastened on anarm155 which is fastened to thebase 39 belonging to theforce frame 41. Thestationary part 153comprises aguide 157 which extends parallel to the Y-direction and along which amovablepart 159 of the secondlinear motor 149 is displaceable. Astationary part 161 of the thirdlinear motor 151 is arranged on themovable part 159 of the secondlinear motor 149 and isprovided with aguide 163 which extends parallel to the X-direction and along which amovable part 165 of the thirdlinear motor 151 is displaceable. As is visible in Fig. 4, themovable part 165 of the thirdlinear motor 151 comprises acoupling piece 167 to which anelectric coil holder 169 of the firstlinear motor 147 is fastened. The firstlinear motor 147 ofthefirst positioning device 21 is, as is the firstlinear motor 69 of thesecond positioningdevice 31, of a kind known from EP-B-0 421 527. Since the firstlinear motor 69 of thesecond positioning device 31 has been described above in detail, a detailed description of thefirstlinear motor 147 of thefirst positioning device 21 is omitted here. It is sufficient to notethat thesubstrate holder 1 is coupled to themovable part 165 of the thirdlinear motor 151exclusively by a Lorentz force perpendicular to the Z-direction during operation. Adifference between the firstlinear motor 147 of thefirst positioning device 21 and the firstlinear motor 69 of thesecond positioning device 31 is, however, that the firstlinear motor147 of thefirst positioning device 21 comprises X-motors and Y-motors of comparablepower ratings, whereas the single Y-motor 123 of the firstlinear motor 69 of thesecondpositioning device 31 has a power rating which is relatively low compared with powerratings of theX-motors 115, 117, 119, 121. This means that thesubstrate holder 1 can not only be taken along by the firstlinear motor 147 parallel to the X-direction overcomparatively large distances, but also parallel to the Y-direction. Furthermore, thesubstrateholder 1 is rotatable about the axis ofrotation 145 by means of the firstlinear motor 147.
• During exposure of thesemiconductor substrate 19, thesubstrate holder1 should be displaced relative to the focusing system 3 parallel to the X-direction with a highpositioning accuracy, while thesubstrate holder 1 is to be displaced parallel to the X-directionor the Y-direction when anext field 35 of thesemiconductor substrate 19 is broughtinto position relative to the focusing system 3 for exposure. To displace thesubstrate holder1 parallel to the X-direction, thecoil holder 169 of the firstlinear motor 147 is displacedparallel to the X-direction by means of the thirdlinear motor 151, a desired displacement ofthesubstrate holder 1 being approximately achieved by the thirdlinear motor 151, and thesubstrate holder 1 being taken along by a suitable Lorentz force of the firstlinear motor 147relative to themovable part 165 of the thirdlinear motor 151. In a similar manner, a desireddisplacement of thesubstrate holder 1 parallel to the Y-direction is approximated in that thecoil holder 169 is displaced parallel to the Y-direction by means of the secondlinear motor149, thesubstrate holder 1 being taken along by a suitable Lorentz force of the firstlinearmotor 147 relative to themovable part 165 of the thirdlinear motor 151. Said desireddisplacement of thesubstrate holder 1 parallel to the X-direction or Y-direction is achievedby means of the Lorentz force of the firstlinear motor 147 which is controlled during thedisplacement of thesubstrate holder 1 by means of the position control system of thelithographic device referred to above, with which a positioning accuracy in the sub-micron oreven nanometer range is achieved. Since the desired displacement of thesubstrate holder 1need be achieved by approximation only by the secondlinear motor 149 and the thirdlinearmotor 151, and accordingly no particularly high requirements are imposed on the positioningaccuracy of the second and thirdlinear motors 149, 151, the secondlinear motor 149 and thethirdlinear motor 151 are, as is the secondlinear motor 71 of thesecond positioning device31, comparatively simple, conventional, one-dimensional linear motors by means of whichthesubstrate holder 1 is displaceable with a comparatively low accuracy over comparativelylarge distances parallel to the Y-direction and X-direction, respectively. The desired accuracyof the displacement of thesubstrate holder 1 is achieved in that thesubstrate holder 1 isdisplaced by the firstlinear motor 147 over comparatively small distances relative to themovable part 165 of the thirdlinear motor 151.
• Since thepositioning device 21 of thesubstrate holder 1 is of a kindsimilar to thepositioning device 31 of themask holder 5, and thestationary part 153 of the secondlinear motor 149 of thefirst positioning device 21 is fastened to theforce frame 41 ofthe lithographic device, as is thestationary part 73 of the secondlinear motor 71 of thesecond positioning device 31, it is achieved that a reaction force exerted by thesubstrateholder 1 on thefirst positioning device 21 during operation and arising from a driving forceexerted by thefirst positioning device 21 on thesubstrate holder 1 is exclusively transmittedinto theforce frame 41. This achieves that the reaction forces of thefirst positioning device21 as well as the reaction forces of thesecond positioning device 31 cause mechanicalvibrations in theforce frame 41, which are not transmitted into themachine frame 45. Sincetheupper surface 141 of thegranite support 143 over which thesubstrate holder 1 is guidedextends perpendicularly to the Z-direction, furthermore, the driving forces of thefirstpositioning device 21, which are also perpendicular to the Z-direction, themselves do notcause any mechanical vibrations in themachine frame 45 either.
• The pattern present on themask 29 is imaged on thesemiconductorsubstrate 19 with said accuracy because themask 29 and thesemiconductor substrate 19 areboth displaceable with said accuracy relative to the focusing system 3 parallel to the X-directionby means of thesecond positioning device 31 and thefirst positioning device 21,respectively, during the exposure of thesemiconductor substrate 19, and because themask 29and thesemiconductor substrate 19 can in addition be positioned parallel to the Y-directionand be rotated about the respective axes ofrotation 67, 145 with said accuracy. The accuracywith which said pattern is imaged on thesemiconductor substrate 19 is even better than thepositioning accuracy of thepositioning device 21, 31 because themask holder 5 is not onlydisplaceable parallel to the X-direction, but is also displaceable parallel to the Y-directionand rotatable about the axis ofrotation 67. A displacement of themask 29 relative to thefocusing system 3 in fact results in a shift of the pattern image on thesemiconductorsubstrate 19 which is equal to a quotient of said displacement of themask 29 and the opticalreduction factor of the focusing system 3. The pattern of themask 29 can thus be imaged onthesemiconductor substrate 19 with an accuracy which is equal to a quotient of thepositioning accuracy of thesecond positioning device 31 and the reduction factor of thefocusing system 3.
• Figs. 7 and 8 show one of the threedynamic isolators 51 in cross-section.Thedynamic isolator 51 shown comprises a mountingplate 171 to which thecornerportion 49 of themain plate 47 of themachine frame 45 resting on thedynamic isolator 51 isfastened. Thedynamic isolator 51 further comprises ahousing 173 which is fastened on thebase 39 of theforce frame 41. The mountingplate 171 is connected via acoupling rod 175 directed parallel to the Z-direction to anintermediate plate 177 which is suspended in acylindrical tub 181 by means of threeparallel tension rods 179. Only onetension rod 179 isvisible in Fig. 7, while all threetension rods 179 are visible in Fig. 8. Thecylindrical tub181 is positioned concentrically in acylindrical chamber 183 of thehousing 173. Aspace185 present between thecylindrical tub 181 and thecylindrical chamber 183 forms part of apneumatic spring 187 and is filled with compressed air through afeed valve 189. Thespace185 is sealed by means of an annular,flexible rubber membrane 191 which is fastenedbetween afirst part 193 and asecond part 195 of thecylindrical tub 181 and between afirstpart 197 and asecond part 199 of thehousing 173. Themachine frame 45 and thecomponents of the lithographic device supported by themachine frame 45 are thus supportedin a direction parallel to the Z-direction by the compressed air in thespaces 185 of the threedynamic isolators 51, thecylindrical tub 181 and accordingly also themachine frame 45having a certain freedom of movement relative to thecylindrical chamber 183 as a result ofthe flexibility of themembrane 191. Thepneumatic spring 187 has a stiffness such that amass spring system formed by the pneumatic springs 187 of the threedynamic isolators 51and by themachine frame 45 and the components of the lithographic device supported by themachine frame 45 has a comparatively low resonance frequency such as, for example, 3 Hz.Themachine frame 45 is dynamically isolated thereby from theforce frame 41 as regardsmechanical vibrations having a frequency above a certain threshold value such as, forexample, the 10 Hz mentioned earlier. As Fig. 7 shows, thespace 185 is connected to asidechamber 203 of thepneumatic spring 187 via anarrow passage 201. Thenarrow passage 201acts as a damper by means of which periodic movements of thecylindrical tub 181 relativeto thecylindrical chamber 183 are damped.
• As Figs. 7 and 8 further show, eachdynamic isolator 51 comprises aforce actuator 205 which is integrated with thedynamic isolator 51. Theforce actuator 205comprises an electric coil holder 207 which is fastened to aninner wall 209 of thehousing173. As Fig. 7 shows, the coil holder 207 comprises an electric coil 211 which extendsperpendicularly to the Z-direction and is indicated in the Figure with a broken line. The coilholder 207 is arranged between twomagnetic yokes 213 and 215 which are fastened to themountingplate 171. Furthermore, a pair of permanent magnets (217, 219), (221, 223) isfastened to eachyoke 213, 215, the magnets (217, 219), (221, 223) of a pair beingmagnetized in opposite directions each time perpendicular to the plane of the electric coil211. When an electric current is passed through the coil 211, the coil 211 and the magnets(217, 219, 221, 223) mutually exert a Lorentz force directed parallel to the Z-direction. The value of said Lorentz force is controlled by an electric controller of the lithographic device(not shown) in a manner which will be explained in more detail further below.
• Theforce actuators 205 integrated with thedynamic isolators 51 form aforce actuator system which is diagrammatically pictured in Fig. 9. Fig. 9 furtherdiagrammatically shows themachine frame 45 and thesubstrate holder 1 andmask holder 5which are displaceable relative to themachine frame 45, as well as thebase 39 and the threedynamic isolators 51. Fig. 9 further shows a reference point P of themachine frame 45relative to which a centre of gravity G_S of thesubstrate holder 1 has an X-position X_S and aY-position Y_S, and a centre of gravity G_M of themask holder 5 has an X-position X_M and aY-position Y_M. It is noted that said centres of gravity G_S and G_M denote the centre of gravityof the total displaceable mass of thesubstrate holder 1 with thesemiconductor substrate 19and that of themask holder 5 with themask 29, respectively. As Fig. 9 further shows, theLorentz forces F_L,1, F_L,2 and F_L,3 of the threeforce actuators 205 have points of applicationon themachine frame 45 with an X-position X_F,1, X_F,2 and X_F,3 and a Y-position Y_F,1, Y_F,2and Y_F,3 relative to the reference point P. Since themachine frame 45 supports thesubstrateholder 1 and themask holder 5 parallel to the vertical Z-direction, thesubstrate holder 1 andthemask holder 5 exert a support force F_S and a support force F_M, respectively, on themachine frame 45 having a value corresponding to a value of a force of gravity acting on thesubstrate holder 1 and themask holder 5. The support forces F_S and F_M have points ofapplication relative to themachine frame 45 with an X-position and Y-position correspondingto the X-position and Y-position of the centres of gravity G_S and G_M of thesubstrate holder 1and themask holder 5, respectively. If thesubstrate holder 1 and themask holder 5 aredisplaced relative to themachine frame 45 during exposure of thesemiconductor substrate19, the points of application of the support forces F_S and F_M of thesubstrate holder 1 and themask holder 5 are also displaced relative to themachine frame 45. Said electric controller ofthe lithographic device controls the value of the Lorentz forces F_L,1, F_L,2 and F_L,3 such that asum of mechanical moments of the Lorentz forces F_L,1, F_L,2 and F_L,3 about the referencepoint P of the machine frame 45 has a value which is equal to and a direction which isopposed to a value and a direction, respectively, of a sum of mechanical moments of thesupport forces F_S and F_M of the substrate holder 1 and the mask holder 5 about the referencepoint P:FL,1 + FL,2 + FL,3 = FS + FMFL,1*XF,1 + FL,2*XF,2 + FL,3*XF,3 = FS*XS + FM*XMFL,1*YF,1 + FL,2*YF,2 + FL,3*YF,3 = FS*YS + FM*YM The controller which controls the Lorentz forces F_L,1, F_L,2 and F_L,3 comprises, for example, afeedforward control loop which is usual and known per se, where the controller receivesinformation on the positions X_S, Y_S of the substrate holder 1 and the positions X_M, Y_M of themask holder 5 from an electric control unit (not shown) of the lithographic device whichcontrols the substrate holder 1 and the mask holder 5, the received information relating to thedesired positions of the substrate holder 1 and the mask holder 5. The controller mayalternatively be provided with a feedback control loop which is usual and known per se,where the controller receives information on the positions X_S, Y_S of thesubstrate holder 1and the positions X_M, Y_M of themask holder 5 from said position control system of thelithographic device, the received information relating to the measured positions of thesubstrate holder 1 and themask holder 5. The controller may alternatively comprise acombination of said feedforward and feedback control loops. The Lorentz forces F_L,1, F_L,2and F_L,3 of the force actuator system thus form a compensation force by means of whichdisplacements of the centres of gravity G_S and G_M of thesubstrate holder 1 and themaskholder 5 relative to themachine frame 45 are compensated. Since the sum of the mechanicalmoments of the Lorentz forces F_L,1, F_L,2, F_L,3 and the support forces F_S, F_M about thereference point P of themachine frame 45 has a constant value and direction, thesubstrateholder 1 and themask holder 5 each have a so-called virtual centre of gravity which has asubstantially constant position relative to themachine frame 45. It is achieved thereby thatthemachine frame 45 does not sense the displacements of the actual centres of gravity G_Sand G_M of thesubstrate holder 1 and themask holder 5 during exposure of thesemiconductor substrate 19. Without the above force actuator system, a displacement of thesubstrate holder 1 or themask holder 5 would lead to an uncompensated change in themechanical moment of the support forces F_S or F_M about the reference point P, as a result ofwhich themachine frame 45 would perform a low-frequency shaking movement on thedynamic isolators 51, or elastic deformations or mechanical vibrations could arise in themachine frame 45.
• The fact that the threeforce actuators 205 are integrated with the threedynamic isolators 51 results in a compact and simple construction of the force actuatorsystem and the lithographic device. The triangular arrangement of thedynamic isolators 51in addition achieves a particularly stable operation of the force actuator system. Since thecompensation force of the force actuator system comprises exclusively a Lorentz force,mechanical vibrations present in thebase 39 and theforce frame 41 are not transmitted to themachine frame 45 through theforce actuators 205.
• The measures discussed above, i.e. the direct introduction of the reactionforces of thepositioning devices 21, 31 exclusively into theforce frame 41, the directcoupling of thesubstrate holder 1 and themask holder 5 to theforce frame 41 exclusively bymeans of a Lorentz force, and the compensation force of theforce actuators 205 have theresult that themachine frame 45 has a supporting function only. Substantially no forces acton themachine frame 45 which change in value or direction. An exception is formed by, forexample, the horizontal viscous frictional forces exerted by the aerostatic bearings of thesubstrate holder 1 and themask holder 5 on theupper surface 141 of thegranite support 143and the plane guides 65 of thesupport member 57, respectively, during displacements of thesubstrate holder 1 and themask holder 5. Such frictional forces, however, are comparativelysmall and do not result in appreciable vibrations or deformations of themachine frame 45.Since themachine frame 45 remains free from mechanical vibrations and elasticdeformations, the components of the lithographic device supported by themachine frame 45occupy particularly accurately defined positions relative to one another. In particular the factsthat the position of thesubstrate holder 1 relative to the focusing system 3 and the position ofthemask holder 5 relative to the focusing system 3 are very accurately defined, and also thatthesubstrate holder 1 and themask holder 5 can be very accurately positioned relative to thefocusing system 3 by means of thepositioning devices 21, 31, imply that the pattern of asemiconductor circuit present on themask 29 can be imaged on thesemiconductor substrate19 with an accuracy which lies in the sub-micron or even nanometer range. Since themachine frame 45 and the focusing system 3 remain free from mechanical vibrations andelastic deformations, moreover, the advantage is created that themachine frame 45 can act asa reference frame for the position control system mentioned above of thesubstrate holder 1and themask holder 5, where position sensors of said position control system such as, forexample, optical elements and systems of said laser interferometer, can be mounted directlyto themachine frame 45. Mounting of said position sensors directly to themachine frame 45results in that the position occupied by said position sensors relative to thesubstrate holder 1,the focusing system 3, and themask holder 5 is not influenced by mechanical vibrations anddeformations, so that a particularly reliable and accurate measurement of the positions of thesubstrate holder 1 and themask holder 5 relative to the focusing system 3 is obtained. Sincealso themask holder 5 can not only be positioned parallel to the X-direction, but can also bepositioned parallel to the Y-direction and rotated about the axis ofrotation 67, whereby aparticularly high accuracy of imaging the pattern of themask 29 on thesemiconductorsubstrate 19 is achieved, as noted above, semiconductor substrates with detail dimensions in the sub-micron range can be manufactured by means of the lithographic device according tothe invention.
• A lithographic device according to the invention was described abovewith asubstrate holder 1 which is displaceable by means of afirst positioning device 21according to the invention, and amask holder 5 which is displaceable by means of asecondpositioning device 31 according to the invention. Thepositioning devices 21, 31 have acommon force actuator system which during operation supplies a compensation forcewhereby displacements of the centres of gravity of both thesubstrate holder 1 and themaskholder 5 are compensated. It is noted that a lithographic device according to the inventionmay alternatively be provided with two force actuator systems with which the displacementsof the centres of gravity of thesubstrate holder 1 and themask holder 5 can be individuallycompensated.
• It is further noted that the invention also covers lithographic deviceswhich work by the "step and repeat" principle mentioned earlier. Thus, for example, apositioning device according to the invention can be used for the displacement of thesubstrate holder in the lithographic device which is known from EP-A-0 498 496 and inwhich exclusively the substrate holder is displaceable over comparatively large distancesrelative to the focusing system. Such a lithographic device covered by the invention is alsoobtained in that thesecond positioning device 31 withmask holder 5 is replaced in thelithographic device discussed in the description of the Figures by a conventional mask holderwhich is stationary relative to themachine frame 45, such as the one known, for example,from EP-A-0 498 496, and in that the compensation force of the force actuator system iscontrolled exclusively as a function of the position of thesubstrate holder 1. The inventionalso covers lithographic devices which work by the "step and scan" principle mentionedabove where the mask holder only is driven by a positioning device according to theinvention, so that the compensation force of the force actuator system is controlledexclusively as a function of the position of the mask holder. Such a construction isconceivable, for example, if the focusing system of the lithographic device has acomparatively great optical reduction factor, so that the displacements of the centre of gravityof the substrate holder are comparatively small relative to the displacements of the centre ofgravity of the mask holder, and the displacements of the centre of gravity of the substrateholder cause comparatively small mechanical vibrations and deformations in the machineframe of the lithographic device.
• The lithographic device according to the invention as described above is used for exposing semiconductor substrates in the manufacture of integrated electronicsemiconductor circuits. It is further noted that such a lithographic device may alternatively beused for the manufacture of other products having structures with detail dimensions in thesub-micron range, where mask patterns are imaged on a substrate by means of thelithographic device. Structures of integrated optical systems or conduction and detectionpatterns of magnetic domain memories, as well as structures of liquid crystal display patternsmay be mentioned in this connection.
• It is further noted that a positioning device according to the inventionmay be used not only in a lithographic device but also in other devices in which objects orsubstrates are to be positioned in an accurate manner. Examples are devices for analysing ormeasuring objects or materials, where an object or material is to be positioned or displacedaccurately relative to a measuring system or scanning system. Another application for apositioning device according to the invention is, for example, a precision machine tool bymeans of which workpieces, for example lenses, can be machined with accuracies in the sub-micronrange. The positioning device according to the invention is used in this case forpositioning the workpiece relative to a rotating tool, or for positioning a tool relative to arotating workpiece.
• Thefirst positioning device 21 of the lithographic device describedcomprises a drive unit with a first linear motor which supplies exclusively a Lorentz force,and a conventional second and third linear motor, while thesecond positioning device 31 ofthe lithographic device described comprises a drive unit with a first linear motor supplyingexclusively a Lorentz force, and a single conventional second linear motor. It is noted thatthe invention also relates to positioning devices provided with a different type of drive unitor a different type of guide. The invention is thus also applicable, for example, to positioningdevices provided with a conventional threaded spindle drive and a straight guide.
• It is finally noted that the force actuator system may have a differentnumber of force actuators instead of the threeforce actuators 205. The number of forceactuators depends on the number of displacement possibilities of the object table of thepositioning device. If the object table is displaceable parallel to the X-direction only, forexample, two force actuators will suffice. Thepositioning devices 21, 31 discussed abovemay also have more than threeforce actuators 205, but the construction would be staticallyoverconstrained in that case.

Claims (12)

1. A positioning device with an object table and a drive unit by which theobject table is displaceable parallel to at least an X-direction over a guide which is fastenedto a frame of the positioning device, characterized in that the positioning device is providedwith a force actuator system controlled by an electric controller and exerting a compensationforce on the frame during operation, which compensation force has a mechanical momentabout a reference point of the frame having a value equal to a value of a mechanical momentof a force of gravity acting on the object table about said reference point, and a directionwhich is opposed to a direction of the mechanical moment of said force of gravity.
2. A positioning device as claimed in Claim 1, characterized in that theobject table is displaceable parallel to a horizontal direction, while the force actuator systemexerts the compensation force on the frame parallel to a vertical direction.
3. A positioning device as claimed in Claim 2, characterized in that theobject table is displaceable parallel to a horizontal X-direction and parallel to a horizontal Y-directionwhich is perpendicular to the X-direction, while the force actuator systemcomprises three force actuators mutually arranged in a triangle and each exerting acompensation force on the frame parallel to the vertical direction.
4. A positioning device as claimed in any one of the preceding Claims,characterized in that the force actuator system is integrated with a system of dynamicisolators by means of which the frame is coupled to a base of the positioning device.
5. A positioning device as claimed in any one of the preceding Claims,characterized in that the compensation force comprises exclusively a Lorentz force of amagnet system and an electric coil system of the force actuator system.
6. A lithographic device with a machine frame which, seen parallel to avertical Z-direction, supports in that order a radiation source (7), a mask holder (5), a focusingsystem (3) with a main axis directed parallel to the Z-direction, and a substrate holder (1) which isdisplaceable perpendicularly to the Z-direction by means of a positioning device,characterized in that the positioning device (21) of the substrate holder is a positioning device asclaimed in any one of the Claims 1 to 5 wherein the frame of the positioning device of thesubstrate holder belongs to the machine frame of the lithographic device, while the force actuator system of the positioning device of the substrate holder exerts the compensationforce on the machine frame.
7. A lithographic device with a machine frame which, seen parallel to avertical Z-direction, supports in that order a radiation source (7), a mask holder (5) which isdisplaceable perpendicularly to the Z-direction by means of a positioning device (31), a focusingsystem (3) with a main axis directed parallel to the Z-direction, and a substrate holder (1) which isdisplaceable perpendicularly to the Z-direction by means of a further positioning device (21),characterized in that the positioning device of the mask holder is a positioning device asclaimed in any one of the Claims 1 to 5 wherein the frame of the positioning device of themask holder belongs to the machine frame of the lithographic device, while the forceactuator system of the positioning device of the mask holder exerts the compensation forceon the machine frame.
8. A lithographic device as claimed in Claim 6, characterized in that themask holder is displaceable perpendicularly to the Z-direction by means of a positioningdevice as claimed in any one of the Claims 1 to 5 wherein the frame of the positioningdevice of the mask holder belongs to the machine frame of the lithographic device, while theforce actuator system of the positioning device of the mask holder exerts the compensationforce on the machine frame.
9. A lithographic device as claimed in Claim 7 or 8, characterized in thatthe positioning devices of the substrate holder and the mask holder have a joint force actuatorsystem such that the value of the mechanical moment of the compensation force of the jointforce actuator system about the reference point is equal to a value of a sum of a mechanicalmoment of a force of gravity acting on the substrate holder about said reference point and amechanical moment of a force of gravity acting on the mask holder about said referencepoint, while the direction of the mechanical moment of the compensation force is opposed toa direction of said sum of mechanical moments.
10. A lithographic device as claimed in Claim 6, 7, 8 or 9, characterized inthat the machine frame is placed on a base of the lithographic device by means of threedynamic isolators mutually arranged in a triangle, while the force actuator system comprisesthree separate force actuators which are each integrated with a corresponding one of thedynamic isolators.
11. A method of manufacturing a semiconductor device using alithographic device having a machine frame that supports in a vertical Z-direction:

    a radiation source (7);

    a mask holder (5);

    a focusing system (3) with a main axis directed parallel to the Z-direction;and

    a substrate holder (1) which is displacable perpendicularly to the Z-directionby means of a positioning device over a guide which is fastened to a frame of thepositioning device that belongs to said machine frame;

       the method comprising the steps of:

    providing a mask to said mask holder;

    providing a substrate at least partly provided with a radiation-sensitive layerto said substrate holder; and

    illuminating said mask and imaging at least a part of a mask pattern of saidmask onto a target portion of said substrate;

       characterised by:
       during or prior to said steps of illuminating and imaging, positioning saidsubstrate holder with said positioning device and exerting a compensation force onsaid frame of said positioning device, which compensation force has a mechanicalmoment about a reference point of the frame having a value equal to a value of amechanical moment of a force of gravity acting on the substrate holder about saidreference point, and a direction that is opposed to a direction of the mechanicalmoment of said force of gravity.
12. A method of manufacturing a semiconductor device using alithographic device having a machine frame that supports in a vertical Z-direction:

    a radiation source (7);

    a mask holder (5) which is displacable perpendicularly to the Z-direction bymeans of a positioning device over a guide which is fastened to a frame of thepositioning device that belongs to said machine frame;

    a focussing system (3) with a main axis directed parallel to the Z-direction;and

    a substrate holder (1);

       the method comprising the steps of:

    providing a mask to said mask holder;

    providing a substrate at least partly provided with a radiation sensitive layerto said substrate holder; and

    illuminating said mask and imaging at least a part of a mask pattern of saidmask onto a target portion of said substrate;

       characterised by:
       during or prior to said steps of illuminating or imaging, positioning saidmask holder with said positioning device and exerting a compensation force onsaid frame of said positioning device, which compensation force has a mechanicalmoment about a reference point of the frame having a value equal to a value of amechanical moment of a force of gravity acting on the mask holder about saidreference point and a direction that is opposed to a direction of the mechanicalmoment of said force of gravity.

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